The present invention relates to a circuit for intermittently driving a DC motor for a clock, wherein the motor is driven by a predetermined exact amount at predetermined time intervals by means of timing pulses, without being affected by the variation in the amplitude of the DC energizing voltage and the variation in the load on the motor, so that the accurate indication of the clock is insured regardless of the variation of the amplitude of the D.C. energizing voltage and the load on the motor.
Heretofore, an AC energizing voltage has been utilized in driving a rotary drum type clock having a plurality of time indicating flaps, each successively brought to the displaying position for indicating the time. An AC synchronous motor is driven directly by the AC energizing voltage, and the continuous rotation of the motor is converted into intermittent motion by means of a mechanical intermittent motion mechanism such as a Geneva gear mechanism or the like. However, such a continuous rotation of the motor has a disadvantage in that it requires a large consumption of the electric power for continuously driving the motor.
Thus, in order to avoid the above disadvantage, a rotary drum type clock has been developed, wherein a DC motor is intermittently driven at predetermined time intervals by a DC energizing voltage by using a timing pulse generating circuit for generating timing pulses at the predetermined time intervals, and the indication of the time is switched each time the DC motor is driven.
However, the timing pulse generating circuit usually comprises IC circuits including a quartz oscillator. The pulse amplitude is affected by the amplitude of the DC energizing voltage although the width and the cyclic period of the pulses are kept unchanged.
Since the DC motor is coupled with the time indicating mechanism of the clock through gearing means, the rotation of the DC motor and hence the rotation of the rotary drum of the clock are varied depending upon the variation in the electric power applied to the DC motor caused by the variation in the amplitude of the pulses even though the load of the motor (the load imposed by the time indicating mechanism) is kept constant, thereby deteriorating the accurate indication of the time.
This results in serious defects in the accurate operation of the clock when a battery of the nominal voltage of 1.5 volts, for example, is used to provide a DC energizing voltage ranging from 1.1 to 1.7 volts in order to most economically or effectively use the electric cell, together with the influence of the variation in the load on the motor resulting from the highest and the lowest load of the time indicating mechanism.
The present invention aims at avoiding the above described disadvantages of the prior art circuit for driving the motor for the clock.